Multi-wire conductor flat ribbon cable is an electrical interconnection economical in cost, space and weight. It is in widespread usage in digital computer systems wherein the multiple conductors of a stripped cable end are soldered directly onto a printed circuit board. To improve the density of the ribbon cable and the associated interconnects to printed circuit lands, small wires are very close together--on the order of 0.0050 inches separation between 0.0095 inches diameter wire conductors. At such densities some stripped conductors of the ribbon cable are often displaceably formed, or bent, into positions above and/or below the plane of the ribbon cable. Such displaced positions permit lower, workable, densities when the wire ends are connected to printed circuit boards.
The most basic and straightforward method of preparing such a ribbon cable end is as follows. The cable is cut to the desired length with the ends square. The insulation is stripped from the conductors about 0.125 inch using a carpenters type wire stripper or the like. The wire ends are individually formed, as selectively desired, by manually aligning each selected conductor between a forming hammer and an anvil form block and individually displaceably forming it as by a manual stroke.
The basic method of end forming the conductors individually, or at most in small groups much less than the total ribbon cable width of 80 or more conductors, is resistant to being improved upon by a solid comb type multiconductor simultaneous forming tool because of tolerance problems. The tolerance problem is that, because the conductor wires are not spaced with exact consistency within the cable and because the width of the cable from first wire to last wire may vary, if a single conductor wire is precisely positioned over a single position of a multiple position simultaneous forming tool then a remote conductor wire, due to spacing variations, will not be in correct position to be controllably correctly formed. In other words, the industry standard workpiece ribbon cable exhibits greater variation across its width than can be tolerated by a solid comb type multiconductor simultaneous forming tool otherwise capable of forming fine conductors at close proximity.
An example of the tolerance problem is that occurring in end forming of a flat ribbon cable of 120 conductor wires of nominal 0.0095 inches diameter and at a nominal spacing of 0.0045 inches between wires. A flat ribbon cable of 120 such wires separated by 119 such spaces would thereby total 1.676 inches from the centerline of the first to the centerline of the last conductor wire. Actual measurements show that this nominal width of 1.676 inches will vary by .+-.0.009 inches. Such a deviation of less than 1% and less than 0.01 of an inch is not surprising for a cable mass produced by the mile. If it is desired to capture the individual wires between the teeth of a comb type block and anvil forming tool so that they may be selectively formed, the teeth must penetrate within the 0.0045 inch spaces. If a first space tooth is exactly centered, the 119th space tooth will not reliably fall into the space between the 119th and 120th wires. If no attempt to separate and guide the conductors is made, as by using only a flat anvil with serration spaces for those selected conductors not to be formed, the problem still exists.
During the explanation of the present inventive solution to this problem, it will be seen that a mechanical device involving two sets of knives will be disclosed as an apparatus for evenly dividing an interval of undetermined and variable length. Prior art utilization of one set of knives exists in a linotype machine. When typeset words, which represent several lengths, are formed across a line of fixed length then the spaces between all such word lengths may be evenly adjusted by forcing separator knives evenly between such word lengths. For example, three knives may be evenly forced into the three spaces between four words on a typeset line in order to effectuate even separation. This function of a knife edge to effectuate even separation will become obvious as the present invention is discussed.
These prior art linotype machine knives will be seen to differ from the present invention which utilizes two intermeshing sets of knives, not one set. The function of the present invention is to divide and partition into various integral multiples of even parts an overall interval of undetermined and variable length, not to evenly separate variable lengths along a fixed interval.